Total Melting Research Articles

Infrared Spectral Classification of Natural Bitumens for Their Rheological and Thermophysical Characterization

Natural bitumens consist of many molecules whose chemical composition depends on the oilfield and determines the physicochemical properties of the bitumens as materials. Infrared (IR) spectroscopy is the fastest and least expensive method to assess the chemical structure of organic molecules, which makes it attractive in terms of rapid prediction of the properties of natural bitumens based on their composition evaluated in this way. In this work, IR spectra were measured for ten samples of natural bitumens significantly different in properties and origin. Based on the ratios of certain IR absorption bands, bitumens are proposed to be divided into paraffinic, aromatic, and resinous. In addition, the internal relationship between IR spectral characteristics of bitumens, such as polarity, paraffinicity, branchiness, and aromaticity, is shown. A study of phase transitions in bitumens by differential scanning calorimetry was carried out, and the use of a heat flow differential to find hidden points of bitumens' glass transitions is proposed. Furthermore, the dependences of the total melting enthalpy of crystallizable paraffinic compounds on the aromaticity and branchiness of bitumens are demonstrated. A detailed study of bitumens' rheology in a wide temperature range was carried out, and characteristic features of rheological behavior for different bitumen classes are revealed. Based on the viscous properties of bitumens, their glass transition points were found and compared with the calorimetric glass transition temperatures and nominal solid-liquid transition points obtained from temperature dependences of bitumens' storage and loss moduli. The dependences of viscosity, flow activation energy, and glass transition temperature of bitumens on their IR spectral characteristics are shown, which can be used to predict the rheological properties of bitumens.

A numerical study on the impact of fin length arrangement and material on the melting of PCM in a rectangular enclosure

This article presents a numerical analysis on enhancing the melting process of phase change material (PCM) in a rectangular enclosure using flanged fins (T-shaped). A double fin arrangement with upper (Lu) and lower (Ld) fins is employed, and various cases based on fin length ratio (Lu/Ld) and material are examined with no-fin PCM enclosure. Copper (Cu), Aluminium (Al) and Carbon steel (C-steel) are selected as the fin material. To assess the effect of flanged fins, five indicators are used; total melting time (tm), total stored energy (Et), average Nusselt number (Nu), mean power (Pm), and cost per mean power (Cpw). The result shows that a high PCM melting rate is observed for a low Lu/Ld ratio, and high thermal conductivity. Hence, Cu fins with Lu/Ld ratio of 0.25 resulted in the high melting, and the tm reached a value of 4050, which is 48.36% less than the no-fin PCM enclosure. While, the Cpw is minimum (0.4 $/W) for both Cu and Al fin at Lu/Ld of 0.25. Overall, Cu fins outperforms other cases and is then further optimized on the variation of Lu/Ld ratio, and flanged to web ratio (Lf/Lu, d). The optimization concludes that a single flanged fin placed at the lower end of the container with Lf/Ld of 0.55 has the minimum tm (2338 s) and Cpw (0.229 $/W).

Volumetric quantification of melting and solidification of phase change materials by in-situ X-ray computed tomography

Solid–liquid phase transitions in phase change materials (PCM) usually exhibit a complex dynamics, which critically determines the performance of latent heat thermal energy storage systems (LHTES). Experimental approaches enabling to track the dynamics of the entire PCM solid–liquid phase transition are thus crucial to provide relevant data for PCM material development and to validate PCM-models used to design efficient LHTES. In this work, we show how in-situ dynamic X-ray computed tomography (XCT) can be used to track the dynamics of the solid–liquid phase transition in PCMs. The method based on time-lapse XCT is illustrated based on data collected for two PCMs (ice/water and calcium chloride hexahydrate) during melting and solidification processes, respectively. Key enabler of the method is the density difference between solid and liquid PCM, which facilitates a clear identification of the solid and liquid PCM phases and, thus, tracking their spatial evolution in time. Analysis of the transient liquid fraction curves reveals a volumetric melting rate of 0.55 (% vol)/min for ice with a total melting time of 165 min, whereas calcium chloride hexahydrate undergoes a partial solidification at −0.30 (% vol)/min, with an overall volumetric shrinkage of 12.7 %. Furthermore, an image-based approach to quantify the time-dependent liquid volume fraction curve from the sequences of XCT imaging data, is presented. The extracted liquid volume fraction curves capture the entire dynamics of the solid–liquid phase transition and can either be directly inserted in the mass and energy balance equations of currently existing PCM models to predict LHTES performance or used for PCM-models validation.

Sensitivity of the Relationship Between Antarctic Ice Shelves and Iron Supply to Projected Changes in the Atmospheric Forcing

AbstractUpward advection or mixing of iron‐rich deep waters due to circulation changes driven by the rate of basal ice shelf melt was shown to be a primary control on chlorophyll a production in coastal polynyas over the Antarctic continental shelf. Here, the effects of atmospheric changes projected in 2100 on this relationship were examined with a 5‐km resolution ocean/sea ice/ice shelf model of the Southern Ocean with different simulated dissolved iron sources and idealized biological uptake. The atmospheric changes are added as idealized increments to the forcing. Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in doubling of the heat advected onto the continental shelf and an 83% increase in the total Antarctic ice shelf basal melt. The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%. However, even though the ice shelf driven contribution becomes less important to the total iron supply on average (29% of total), the ice shelf involvement becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas. The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers. These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come.

Investigation and optimization on melting performance of a triplex-tube heat storage tank by rotational mechanism

Phase change heat storage is the backbone of energy storage technology, but its storage time is affected by the low thermal conductivity of phase change materials. Therefore, the melting performance of a triplex-tube latent heat thermal energy storage unit (T-LHTESU) in a phase change heat storage system is studied in this paper, and the rotation mechanism is applied to the unit. Firstly, a numerical model of the T-LHTESU considering the rotation mechanism is constructed, and the validity of the rotation unit is verified by comparison with experimental data. In this unit, N-eicosane is used as a phase change material for heat exchange. The effects of different rotational speeds on the liquid phase distribution, temperature distribution, flow velocity distribution, total energy storage, and energy storage efficiency of the T-LHTESU are studied. The results show that the melting time of this unit at 0.1 and 1 rpm is 46.98 and 69.35% lower than that of the stationary model, respectively. The total amount of stored heat is decreased by 0.67 and 2.17%, and the heat storage efficiency is increased by 87.34% and 219.19%, respectively. This indicates that the addition of the rotation mechanism greatly increases the heat storage efficiency of the T-LHTESU and reduces its total melting time, while the reduction of the total energy stored in the melting cycle is small. Then it is proved that rotation improves the single heat transfer mechanism of the stationary model and eliminates the thermal deposition caused by natural convection by studying the internal temperature/velocity response of the stationary model and the speed of 0.1 rpm. The related geometric structure of the model is optimized by response surface optimization design based on 0.1 rpm rotation speed. The influence of each variable on the target response is obtained, and compared with the original model, the melting time of the optimized model is reduced by 12.24%. Finally, based on the geometric optimization design, the influence of element physical factors (temperature and material of fin/tube wall) on the related melting properties is studied. This study is helpful to promote the effective use of rotation mechanism in phase change heat storage systems and has a certain guiding role in the structural design.

Assessment on the melting performance of a phase change material based shell and tube thermal energy storage device containing leaf-shaped longitudinal fins

This work concerns the development of a leaf-shaped longitudinal fin for the melting performance enhancement in a shell and tube thermal energy storage device. A two-dimensional code with the consideration of natural convection is established to simulate the phase transition process in phase change material (PCM), and the reliability is validated through comparing of the numerical results with published experimental data. The dynamic temperature evolution and response of the leaf-shaped fin with enhanced performance is first analysed. The effects of the fin length, fin angle and fin material on the melting performance are then studied and discussed. Finally, the fin shape effect on PCM melting process is assessed by considering two different configurations of rectangular and triangular sub-branches under the same working conditions. The results show that the leaf-shaped fin with ever-increasing length of sub-branches offers extra thermal surface to contact the PCMs that located at the far side of the heating source, and hence achieves uniform heat transfer rate and accelerates the melting process in the device. For a fixed fin volume in the device, the fin length exhibits significant influence on the melting rate with the complete melting duration being shortened by 14.2 % when the value varies from 22 mm to 25 mm. Moreover, the performance enhancement induced by the leaf-shaped fin can be further strengthened by optimizing the fin sub-branch angle and shape. It is revealed that the fin with a branch angle of 75° achieves an acceleration of whole melting process by 12 % compared to the fin with branch angle of 90°. The total melting time in the fin with triangular shape of sub-branches can be reduced by 30.1 % in comparison with the fin with rectangular configuration of sub-branches.

Effect of twisted fins on the melting performance of PCM in a latent heat thermal energy storage system in vertical and horizontal orientations: Energy and exergy analysis

• Performance of a LHTES unit in the presence of twisted fins is studied. • Different number of fins in vertical and horizontal orientations were considered. • Paraffin wax was used as PCM. • Triple fin and double fin outperformed other cases in vertical and horizontal cases. • The best case is a trade-off between the fin number and length of fins. Solar energy and other renewable energy resources are of great importance to solve the energy crisis in the 21th century. In this regard, the energy storage systems play a vital role as a means of harnessing solar energy. In this study, performance enhancement of a shell and tube latent heat thermal energy storage (LHTES) system in terms of energy and exergy has been assessed by implementing twisted fins in a PCM enclosure with both vertical and horizontal orientations by using Finite Volume Method and the Enthalpy-Porosity method has been used for simulating the melting process. The fins have constant heat transfer surface with different configurations including single, double, triple and quadruple fins along with a case study about effect of penetrating the fin inside the tube. Paraffin wax was used as PCM. The results have been presented in terms of melt fraction, temperature and velocity magnitude contours, melt fraction and temperature curves, average Nusselt number and total melting time for both horizontal and vertical orientations. In order to better evaluate the optimizations made, exergy analysis has also been performed and the exergetic efficiency has also been presented. It was revealed that the triple fin in vertical orientation and double fin in horizontal orientation have the best effect on melting enhancement of PCM with 11.2% and 10.7% of enhancement in melting time in comparison with the worst finned case, and 37.4% and 30.5% enhancement in comparison with the base case. It was also shown demonstrated that the triple fin in vertical orientation and double fin in horizontal orientation have the best exergy efficiency.

Synergistic improvement of melting rate and heat storage capacity by a rotation-based method for shell-and-tube latent thermal energy storage

• Convection is enhanced with the lower-half PCM rotated to the top. • Low-speed rotation can’t avoid deterioration of uniformity caused by reverse flow. • High-speed rotation could be equivalent to the single rotation when f R =0.5. • Liquid fraction is chosen for judging the moment of executing single rotation. • Effects of single rotation enhance with the increase of LTES size. Rotation is emerging as a novel heat transfer enhancement technique for latent thermal energy storage (LTES) due to its superiority in concise control of rotation conditions and significant effects of heat transfer enhancement. However, the detailed mechanism of heat transfer enhancement triggered by rotation and optimization of rotation conditions have been hardly concerned and explained in previous studies. This study aims to illustrate the effects of rotation on the total melting time, heat transfer rate as well as temperature uniformity of LTES during the heat storage process. Firstly, the effects of constant rotation on the heat storage process are investigated. Then the single rotation of 180° is proposed and effects of the moment to implement the rotation are discussed. Finally, the effects of the single rotation of 180° are examined under different sizes of LTES. Results indicate that convection caused by rotation inside the LTES enhances the melting process, and the effects enhance with the increase of rotation speed. It is also found that the 180° inversion of LTES significantly improves the intensity and range of convection, which has similar effects to the constant rotation. Quantitively, applying the single rotation when f R =0.5 leads to the maximum reduction in total melting time of 533.7%, which is close to the 610.3% for the case with the highest rotation speed of 1 rpm. The positive effects of single rotation on enhancing the melting rate and heat storage density become much more obvious under the larger size of LTES.

Energy storage performance improvement of phase change materials-based triplex-tube heat exchanger (TTHX) using liquid–solid interface-informed fin configurations

The future of power generation is predicted to be greener with greater uptake in renewable energy which will be more intermittent and make matching demand harder. Latent thermal energy storage using phase change materials (PCMs) could provide a solution to that problem. PCMs can store large amounts of energy in small volumes, however, the main issue is the low conductivity of PCMs, which limits the rate that energy can be stored due to the slow melting and solidification processes. In the present study, we design and optimise a flow structure-informed fin configuration for triplex-tube heat exchangers (TTHXs) that accelerates the PCM melting process to allow for faster energy storage rates. The computational fluid dynamics modelling is developed to evaluate different TTHX geometries and find the most efficient fin geometries. The results show that an optimal fin geometry can provide a 57.4 % reduction in melting time, which demonstrates that fins offer a very effective way of reducing the melting times of PCMs without taking up much volume. We also found that fins in the lower half of the PCM are more effective in reducing total melt time than fins in the upper half. It is revealed that curved fins offer better performance when compared to similar straight fins. Lastly, it is observed that horizontal or angled surfaces allow for more natural convection in TTHX. The findings can be used to inform future studies on energy storage performance improvement of PCMs.

Assessment on the effect of longitudinal fins upon melting process in a latent heat thermal energy storage unit

Latent heat thermal energy storage(LHTES) unit are an effective technical means to balance the demand and supply of energy. To enhance the heat transfer efficiency of the phase change material(PCM) in the LHTES unit, a series of novel three-tube heat exchangers with longitudinal fins was designed. The study was carried out in terms of the number, length, thickness, and arrangement of fins. Results demonstrate that the thickness change of fins has a significant effect on reducing the melting time of the whole PCM. The thin long fins have a higher melting rate. The complete melting time of the thin long fins was 10.6 % faster than that of the short thick fins. By studying the effect of fin length on the heat storage performance, it was found that the structure appeared to be more reasonable at L = 30 mm and the heat storage time was shortened by 18.0 %. In addition, the use of the lower long and upper short fin arrangement can strengthen the heat transfer. Considering that the amount of heat storage capacity decreases as the number of fins increases, N = 20 is considered as the best fin number. Therefore, we give an optimal combination of fin design parameters (N = 20, L = 30, W = 1), which shortens the total melting time of PCM by 71.2 %. To be conclusive, it is more beneficial to add fins to heat transfer enhancement than to have no fins, saving more energy charging time.

The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

Abstract. The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero, and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and output of the Antarctic Mesoscale Prediction System (AMPS) on a 1.7 km grid are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events causes foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier, and melt often occurs with subzero air temperatures. During foehn events, melt rates are enhanced, contributing to 23 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn, through an increase in turbulent mixing resulting from gustier and warmer wind conditions, is largely compensated for by extra heat losses through sublimation. Melt rates are enhanced through an additional energy surplus from a reduced albedo during foehn.

Local optimization strategy of copper foam on heat transfer enhancement for phase change materials

It is a promising method to achieve the high thermal storage rate and density of phase change materials (PCMs) by embedding metal foam into them. However, a solid region (which is always called the “dead region”) of the PCMs is normally formed due to the natural heat convection at the final melting process. To address this issue, a special cascaded copper foam configuration is incorporated into the PCMs to enhance heat transfer of the local “dead region”. The local optimization strategy is investigated by considering the local filling direction, ratio, and porosity of copper foam. The results show that the melting rate and temperature response of the composite PCMs are improved by tailoring the local porosity in the cubic container. For instance, the total melting time is reduced by up to 14.2 % when the local porosity is lowered to 86 %. The low-porosity copper foam filled parallel to the horizontal heat flow has better effects on local enhancement than that filled vertically. Moreover, the optimal local filling ratio of copper foam increases with the local filling porosity. For example, the optimal local filling ratio is 60 mm for copper foam with a porosity of 86 %, and 100 mm for that with a porosity of 94 %. This study provides a local optimization strategy to enhance the properties of composite PCMs by embedding metal foam.

Structure Optimization of Longitudinal Rectangular Fins to Improve the Melting Performance of Phase Change Materials through Genetic Algorithm

In this paper, the structural parameters of longitudinal rectangular fins used in a horizontal shell-and-tube latent heat storage unit (LHSU) are optimized to increase the melting rate of phase-change materials. The influence of natural convection on the melting process is considered. Due to the extremely nonlinear and expensive computational cost of the phase-change heat-transfer-optimization problem, a new coupling algorithm between genetic algorithm and computational fluid dynamics is developed. The effects of the thermal conductivity of fins; the filling rate of fins; and the number of fins on the optimal structure parameters, including the length, width, and position of each fin, are discussed. The results show that when a single fin is inserted in the half-ring region, the optimal dimensionless fin angle is about 0.2, and the optimal dimensionless fin length is about 0.96. The use of optimal single fin can shorten the dimensionless total melting time by 68% compared with the case of no fin, and 61.3% compared with uniformly arranged single fin. When the number of fins exceeds one, each fin should have a specific length (L), thickness (∆), and position (ψ) instead of uniform distribution. The advantage of the optimized fins decreases as the number of fins increases. When the number of fins is four, the optimized fin distribution is almost uniform, and the dimensionless total melting time is only 15.9% less than that of the absolutely uniform fin. The number of fins is a more sensitive parameter affecting the optimal position and structure of fins than the filling rate and thermal conductivity of fins.

Accelerating High-Fidelity Thermal Process Simulation of Laser Powder Bed Fusion via the Computational Fluid Dynamics Imposed Finite Element Method (CIFEM)

• A finite element (FE) method is proposed to accelerate high-fidelity scanwise thermal process simulation in laser powder bed fusion (L-PBF) • Computational fluid dynamics (CFD) thermal fields are predicted by a dimensionality reduction based deep learning framework • Predicted thermal fields are imposed on the finite element (FE) solution domain within a relatively small region encompassing the melt pool, while heat diffusion effects elsewhere are solved via the FE method • The FE solution precisely matches the CFD solution across all melting regimes • The FE model running on a GPU card with 4,608 CUDA cores is 28.2x more efficient than the CFD simulations running on 24 CPU cores in parallel The current work proposes a finite element method (FEM) to accelerate scanwise thermal process simulation of the laser powder bed fusion (L-PBF) process with computational fluid dynamics (CFD) resolution near the melt pool. Termed the CFD imposed FEM (CIFEM), the transient thermal fields from a high-fidelity CFD simulation and inferred by deep learning are imposed as temperature values rather than utilizing a conventional heat source model as in existing FEM-based process simulations. These fields are enforced only within a relatively small computational region encompassing the melt pool, while heat diffusion effects elsewhere are solved via the FEM. For a wide range of laser power and scan speeds covering the conduction, transition, and keyhole melting regimes, 29 of the 30 total CIFEM-simulated melt pool sizes lie within two standard deviations of the experimental melt pool sizes. Compared with the CFD simulations, the thermal fields obtained by CIFEM possess 7.44% mean absolute relative error (MARE), significantly less than the 43.76% MARE on three representative test cases simulated using the Goldak heat source model calibrated to the measured melt pool dimensions. In terms of computational efficiency, the CIFEM model running on a GPU card with 4,608 Compute Unified Device Architecture (CUDA) cores is 28.2x more efficient than the CFD simulations running on 24 CPU cores in parallel.

Effect of fins on melting of phase change material in a closed vertical cylinder under microgravity

In this study, the melting dynamics of a phase change material (PCM) filled in a closed vertical cylinder under microgravity are investigated numerically, and the results are compared with the melting dynamics of PCM under gravity. In addition, the effect of inserting fins inside the PCM unit under microgravity on melting dynamics is evaluated. A three-dimensional symmetric numerical model is developed to analyze temperature field, fluid flow, and melting front profile, as well as heat flux, melting time, power, stored energy and stored energy per mass during the melting of PCM RT27 under microgravity field. The results show that the melting performance of PCM in the microgravity field is lower than in the gravity field. The melting process is 64.7% slower in the case of the PCM unit under microgravity compared to the PCM unit under gravity. However, when the fins are inserted into the PCM unit, the melting is accelerated. The reduction of the total melting time of the PCM under microgravity is 78.8%, 58.1%, and 30.7% for the non-dimensional fin widths of 0.8, 0.6, and 0.4, respectively, compared to the no-fin configuration. When the fins are inserted, the amount of energy per mass is decreased, but the power increases dramatically. For the non-dimensional fin width of 0.8, the decline in the energy per mass is the highest, which is 17.6%, and the increase in the power is the highest, which is 349.4%.

Beryllium melt instabilities and ejection during unmitigated current quenches in ITER

The dynamics of transient liquid beryllium flows induced on the ITER first wall during the current quench stage of unmitigated vertical displacement events are modelled by means of two-dimensional Navier–Stokes simulations. The study focuses on melt that is driven to the first wall panels’ chamfered edges, where free-surface instabilities are the most likely to be seeded. Beyond their impact on plasma-facing component damage, these instabilities potentially result in material ejection in the form of droplets, which may ultimately solidify into dust and accumulate in the vessel. Based on prior integrated numerical predictions of quenching magnetic equilibria, wall energy deposition and melt-related damage in a concrete worst-case disruption scenario, the simulations suggest that, although the liquid layer is significantly destabilized, only 5% of the total melt mass created on the wall surface is lost through ejection. This result can serve as a basis to refine the estimates of the real transient-induced beryllium dust inventory expected in ITER.

Spatiotemporal change analysis for snowmelt over the Antarctic ice shelves using scatterometers

Using Scatterometer-based backscatter data, the spatial and temporal melt dynamics of Antarctic ice shelves were tracked from 2000 to 2018. We constructed melt onset and duration maps for the whole Antarctic ice shelves using a pixel-based, adaptive threshold approach based on backscatter during the transition period between winter and summer. We explore the climatic influences on the spatial extent and timing of snowmelt using meteorological data from automatic weather stations and investigate the climatic controls on the spatial extent and timing of snowmelt. Melt extent usually starts in the latter week of November, peaks in the end of December/January, and vanishes in the first/second week of February on most ice shelves. On the Antarctic Peninsula (AP), the average melt was 70 days, with the melt onset on 20 November for almost 50% of the region. In comparison to the AP, the Eastern Antarctic experienced less melt, with melt lasting 40–50 days. For the Larsen-C, Shackleton, Amery, and Fimbul ice shelf, there was a substantial link between melt area and air temperature. A significant correlation is found between increased temperature advection and high melt area for the Amery, Shackleton, and Larsen-C ice shelves. The time series of total melt area showed a decreasing trend of −196 km2/yr which was statistical significant at 97% interval. The teleconnections discovered between melt area and the combined anomalies of Southern Annular Mode and Southern Oscillation Index point to the high southern latitudes being coupled to the global climate system. The most persistent and intensive melt occurred on the AP, West Ice Shelf, Shackleton Ice Shelf, and Amery Ice Shelf, which should be actively monitored for future stability.

Study of the Phase-Change Thermal-Storage Characteristics of a Solar Collector.

A combined solar phase-change thermal-storage heating system is proposed, wherein erythritol is used as the phase-change material (PCM) used to fill the thermal-storage device, and the storage cavity is heated and stored with a disc concentrator. The Solidification/Melting, Volume-of-Fluid (VOF) model of ANSYS Fluent software was used to simulate the phase-change process of erythritol inside the thermal-storage device. The thermal-storage device was designed based on our numerical calculations, and its performance was tested. We found that larger PCM-volume fractions correlated with lower PCM volume-expansion rates and longer total melting times during the heat storage process. When the φ value equaled 80%, the PCM solid-liquid-phase interface and temperature distribution were most uniform and showed the best heat storage. In addition, the size of the heat-storage device affected the heat-exchange area, and the total melting time of the PCM decreased and then increased as the width-to-height ratio (I) increased. With this design capacity, the late stage of the charging process of the heat-storage device accounted for 70% of the total time, and the heat energy-utilization rate during the boiling process was 66.3%. Overall, this combined heating system can be considered a very efficient solar energy-utilization terminal for basic domestic energy needs.

Regulation mechanism of magnetic field on non-Newtonian melting and energy storage performance of metal foam composite nano-enhanced phase change materials

A numerical study is conduced to explore regulation mechanism of magnetic field on melting heat transfer and energy storage performance of nano-enhanced phase change material (NEPCM) composited with metal foam. The enthalpy-porosity method, Darcy-Forchheimer model and local thermal non-equilibrium model are used to describe melting process, flow in porous media and coupling heat transfer, respectively. The proposed model is then verified by experiments using thermochromic liquid crystal thermometry. Effects of nanoparticles mass fraction (0%≤Φwt≤5%), magnetic number (0≤Mn≤7×106), and Rayleigh number (104≤Ra≤106) on the non-Newtonian fluids flow, melting heat transfer and energy storage characteristics are illustrated and discussed. Results show that the addition of Fe3O4 nanoparticles can effectively promote melting and induce non-Newtonian effect of molten NEPCM, but Φwt has no significant influence on the heat transfer. With the increase of Mn, the suppression effect of magnetic field on the whole melting process of NEPCM enhances at moderate Ra = 105, and natural convection is fully developed with a “force bridge” phenomenon of Kelvin force. For lower Ra (=104), natural convection becomes weaker and magnetic field presents a “force loop” phenomenon. For larger Ra (=106), natural convective heat transfer has absolute predominance and the suppression effect of magnetic field can be ignored. Moreover, the increase of Φwt and Ra have obvious positive contributions to heat storage and heat storage efficiency. At low Ra, the suppression effect of magnetic field on heat storage and total melting time leads to decrease in energy storage efficiency.

Melting behavior and heat transfer performance in a modified PCM-filled enclosure with fins under hypergravity conditions

The latent heat energy storage (LHTES) system has been suggested for the thermal management of airborne equipment due to its superior thermal energy storage capability. The enthalpy-porosity method is used to investigate the melting heat transfer characteristics of phase change material (PCM) in embedded fin enclosures under hypergravity. The effects of different hypergravity values and directions on the melting process are analyzed. The results indicate that the melting is greatly accelerated by the fin due to its high thermal conductivity. Compared with the enclosure without fins, the addition of fins reduced the melting time by a maximum of 46.0%. Under the hypergravitational environment, natural convection is significantly enhanced, which leads to a more than 5 times increase in the maximum velocity of the liquid PCM as the gravity value increases from 1 g to 9 g. The direction of hypergravity also affects the heat transfer performance. Under hypergravity values of 5 g, the total melting time at θ = 0° is reduced by 60.24% compared to the case of θ = 90°. The findings of this study may contribute to the design of the LHTES system in aerospace applications.